Electric circuit interrupter



Nov. 12, 1963 H. N. SCHNEIDER ETAL ELECTRIC CIRCUIT INTERRUPTER Filed May 9, 1961 Attovn-eg.

3,110,7t ELECTRIC ClRCUlT INTERRUPTER Harold N. Schneider, Springiield, and Ernest H. Bogert, Media, Pa., assignors to General Electric Company, a corporation of New Yori:

Filed May 9, 1961, Ser. No. 1%,813

6 Claims. (Cl. 20d-144) This invention relates to electric circuit interrupters, and more particularly it relates to an electric arc extinguisher of the type employ-ing spaced metal plates.

Electric circuit interrupters are used to interrupt the flow of current in electric power circuits. The current interrupting action is begun by separating cooperating contact members of the interrupters contact structure, whereby a gap of air or gaseous matter is opened in the circuit. The gases in .the gap between the separated contacts, although normally having relatively great dielectric strength or insulating ability, may temporarily be rendered electrically conductive due to the phenomenon of ionization. If there is simultaneously a sutiicient potential ditierence lbetween the separated contacts and a sutilcient degree of ionization of the gases in the gap, the ionized gases will form an elect-ric arc which must be permanently extinguished in order to interrupt lthe circuit current.

' One form of electric arc extinguisher, or arc chute, in common use for many years employs a series of spacedapart metal barriers or plates in order to extinguish the arc drawn by separable contacts of the circuit interrupter. The met-al plates span insulating sidewalls enclosing the arc and are stacked transversely across the course which the arc will ffollow, as it extends from the region of arc initiation, whereby the arc irnpinges upon the exposed leading edges of the metal plates `and is chopped or divided into -a family Lof `serially related sections which are subsequently deionized and extinguished while moving within the interplate spaces. Such arc-intercepting metal plates contribute to the -arc quenching process in several diiierent ways. Their relatively cool surfaces reduce the temperatures of the arc thereby enhancing deionization and increasing arc resistance. The plates cause a turbulent mixing of the hot arc gases and the relatively cool air in the spaces Ithrough which the arc sections move, thereby urther enhancing deionization. Each section of the arc has its own anode and cathode voltage drop region where the voltage gradient is relatively high; in other words, a thin'cathode or anode sheath of relatively high dielectric strength is formed adjacent the opposing faces of each pair of metal plates, and at least a' certain minimum potential difference between adjacent plates is required in order to sustain or re-establish the associated arc section. Accordingly, the cumulative effect of a plura-lity of spaced metal plates is to so impair the conductivity of the current path -in the arc extinguisher that the arc is quickly and permanently extinguished.

ln order to increase the interrupting rating and to reduce the interrupting time of spaced metal-plate type arc extinguishers, it has previously been proposed to arrange large numbers of the arc-intercepting plates in at least two distinct stacks or groups disposed at different locations along the periphery of the loop-shaped course which the arc follows. Such an arrangement is shown, for example, in Patent No. 1,904,463-Hi1liard, issued on April 18, 1933, and in Patent No. 2,861,152-Scul1y, issued on November 18, 1958. For reasons of mounting convenience, or, :as is suggested in the Scully patent, in order to provide an adequate venting or exhaust port between plates most remote from .the region of arc initiation, a relatively large gap may be left between the different groups of metal plates. With such construction there has United States Patent() 3,110,799 Patented Nov. l2, 1963 ICC been a real possibility that an arc section might undesirably blow through the relatively large gap which separates adjacent groups of plates, and it is a general object of the present invention to provide improved means for effectively precluding such a possibility.

Another problem .sometimes encountered in metalplate type arc extinguishers is the reformation or restriking of :a continuous arc across the trailing edges of the arc-intercepting plates. fl'his problem has been effectively solved by the utilization of an insulating bathe in the manner taught and claimed by Vincent N. Stewart in Patent No. 3,013 1,552. granted on April 24, 1962. In accordance with Stewamts teaching, yat least one of the spaced metal pilates of the arc extinguisher is made shorter than the two companion plates adjacent thereto, and `a coplanar insulating plate-spanning the sidewalls of the arc extinguisher and overlapping the trailing portions of said ltwo adjacent plates-is disposed in edgewise engagement with the trailing edge of the short plate. In this particular location the insulating plate provides an impediment in the shortest path across `the trailing edges of the metal pilates, and the objectionable restriking is prevented. We have found in an arc extinguisher of this sort, when subjected to severe dntenrupting duty, that the arc sections terminating on the short metal plate wil-l sometimes run toward the corners of the trailing edge of this plate where they may soon erode and vaporize the metal, damage the corresponding corners of the associated insulating plate, and damage the adjoining surfaces of the insulating sidewalls as well. Accordingly, therefore, another object of the present invention is the provision, in an arc extinguisher having arc-intercepting metal plates backed up by insulating plates in edgewise association therewith, of means for encouraging the arc to seek a median course between the sidewalls of the arc extinguisher.

Another object of the invention is the provision, in an arc extinguisher having a plurality of spaced-apart arcintercepting metal plates arranged in at least two groups, of improved means for stabilizing the arc in between the two groups of plates and in between the sidewalls of the extinguisher.

In carrying out the invention in one form, an electric arc extinguisher is provided with a pair of spaced sidewalls which idene an afrcing chamber in the vicinity of a region of arc initiation. The arc, which is initiated by the `separation of circuit interrupting contacts, will follow an expanding generally loop-shaped course, and `across this course, spanning the sidewalls, a plurality of spacedapart metal plates are disposed. Consequently the arc impinges upon the exposed leading edges of the metal plates and is chopped thereby into serially related sections. Tne metal plates are arranged in at least two groups with the two plates at the proximate ends, respectively, of the two groups being separated by -a relatively large gap, .and in that gap there is `disposed an arcintercep-ting metal member for `dividing the arc section between the aforesaid end plates into two arclets. The arc-intercepting metal member is so shaped and located that the terminals of said -arclets attached to it advance normally to the loop-shaped :course of the arc at a slower rate than the arclet terminals attached to the two end plates, respectively, thereby creating a concavity in the larc loop. With this arrangement, the arc is effectively stabilized between the two groups of metal plates and will not blow through the relatively large gap left therebetween.

In one aspect of the invention the aforesaid arc-intercepting member is located centrally between the sidewalls, from both `of which it is separated by insulating media. Preferably Iat least `one of the spaced metal plates of the arc extinguisher has in edgewise association with `its trailing edge an insulating plate which spans the sidewalls of the extinguisher in generally coplanar .relationship with the yone metal plate. The trailing edge of the one metal plate is provi-ded with a generally convex contour, and the cooperating edge 'of the associated insulating plate is provided with Ia matching concave contour, so that midway between the sidewalls said trailing edge -is more remote from the region of arc initiation than are portions of the trailing edge next to the sidewalls. With this arrangement the arc sections in the interplate spaces are kept away from the ysidewalls of the extinguisher as they advance to the trailing edge of the one plate. i

The invention will be better understood and its various objects and advantages will be more fully appreciated Ifrom the following description taken into conjunction with the accompanying drawing in which:

FIG. l is a side elevation, partly in section, of a circuit interruptor embodying a preferred form of the invention;

FIG. 2 is an enlarged sectional view of a portion of the arc extinguisher of FIG. l taken along the line 2-2;

PIG. 3 is a further enlarged partial sideview of the portion of the arc extinguisher shown in section in FIG. 2; and

FIG. 4 is la front elevation of two coplanar plates taken from the arc extinguisher of FIG. 1.

Referring now to FIG. 1, we have shown for the purposes of illustration an arc extinguisher or `arc chute 11 for a 'circuit interruptor of a type that may be used in direct current electric power circuits. It should Ibe understood at the outset that our invention is not limited to ldirect current circuit interrupters, and it may be applied to alternating cur-rent interrupters as well. However, the specific circuit interrupter that has been shown in order to best illustrate the present invention is particularly well suite-d for use as an anode breaker in a power rectifier system. As such, the interruptor may be called upon to interrupt unidirectional arc-back current which rises lat an extremely high rate, such as 14,000,000 amperes per second, to aA very large peak magnitude. In this application it is important to interrupt the arcback current lat a relatively low magnitude (under 70,- 000 amperes, 4for example) before it reaches the available peak, and therefore the :arc extinguishing process in the arc chute 11 must be completed in an extremely short time.

The particular circuit interrupter illustrated in FIG. 1 includes la simplified showing of the contact structure which is described in detail and claimed in Patent No. 2,329,003 issued to J. W. Seaman on September 7, 1943. This structure comprises an upper terminal stud assembly 12 on which is movably supported a plurality of relatively stationary main contacts 13, only one of which appears in FIG. 1, land 'a stationary arcing contact 14. Cooperating with the relatively stationary main contact 13 is a movable main contact 15, and cooperating with the stationary arcing contact r14 is :a movable arcing contact 16. The movable main contact -15 is mounted for pivotal movement with respect to a supporting frame member 17.

Both of the movable main and yarcing contacts 15 and 16 are electrically connected to la lower terminal stud 1S of the circuit interruptor. The circuit interruptor is shown -as ybeing supported on a base 19 of suitable insulating material. In order to interrupt the fiow of current in an external electric power circuit (not shown) connected to the upper and lower terminal studs -12 and yand 18, the cooperating movable and stationary members of the contact structure `are separated by means of a suitable operating mechanism (not shown) coupled to the movable contacts by an actuating member 20, and in FIG. l the contacts have been shown in their separated or open circuit position. t

As can be seen in FIG. l, the arc extinguisher 11 is adapted to be mounted on the circuit interrupter adjacent to and principally above the arcing contacts 14 and d6. The arc extinguisher comprises a pair of spaced sidewalls 2,1 and 22 of suitable insulating material for enclosing the arc drawn between the contact members 14 and 16 upon separation thereof. The inner surfaces of the sidewalls 21 and 22 define an arcing chamber in the vicinity of the region of arc initiation, these sidewalls being parallel to the course which the arc will follow as it moves upwardly in the extinguisher 11.

Between the sidewalls 21 and 22 adjacent to their left and right hand edges, as viewed in FIG. 1, transverse endwalls 23 and 24 of insulating material are disposed. The transverse endwall 23 is secured to the base 19 of the circuit interrupter, and the endwall 24 is fastened to the sidewalls 21 and 22 by suitable means, such as the bolts shown at 25 in FIG. l. The sidewalls 21 and 22 are overlaid by bracing plates 26 and 27, respectively, of mechanically stronger material. The plates 25 and 27 are fastened to the sidewalls at one end by means of two of the bolts 25 and at the opposite end by two additional bolts 2%, with an -appropriate spacer, through which the bolts 218 extend, being disposed between the sidewalls immediately above the base 19.

The endwalls 23 and 24, which determine the spacing between the sidewalls 21 and 22 of the arc extinguisher 1.!1, extend divergently outwardly from the vicinity of the circuit interruptor contact structure toward a relatively large exhaust outlet along the top of the arc extinguisher where the arc products are discharged. The endwalls 23 and 24 support on their inner sides a pair of arc runners 29 and 30, respectively. `Ihe lower end of the arc runner 30 is bent around the bottom of the end wall 24 in order to facilitate the transfer of the arc terminal from the movable arcing contact 16 to this arc runner during the circuit opening operation of the interrupter, and it is electrically connected to the lower terminal stud 1S by a connection bar 31. The stationary arcing contact 14 is mounted on the lower end of the companion arc runner 29, and this arc runner may be electrically connected to the upper terminal stud 12 by a suitable flexible conductor, not shown.

Each of the arc runners 29 and 30 is narrow relative to the width of its supporting endwall, and consequently the arc runners are spaced away from both of the sidewalls 21 and 22. For protecting the endwalls 23 and 24 against the eroding action of the arc terminals as they travel along the arc runners, relatively wide protective sheets 3-2 of high arc-resistant insulating material are inserted between the endwalls and the arc runners supported thereon.

When the cooperating movable and stationary contacts are separated or opened while the circuit interruptor is carrying current of substantial magnitude, the gases in the resulting gap become ionized and an electric arc is established. Due to the combined infiuence of several factors, the stream of ionized gases comprising the arc follows an expanding generally loop-shaped course as it is driven or propelled away from the point of arc initiation toward the outlet or discharge end of the arc extingusher 11. The central portion of the arc, being unirnpeded, moves more rapidly through fthe extingusher than the terminals or roots of the arc which require extra time to establish new arc spots as they advance along the metal arc runners 29 and 30, and the magnetic effect of the arc loop tends, in a Well-known manner, to expand the loop. Thus, a looping arc of gradually extending length rises in the arc extinguisher toward its exhaust outlet, as indicated in FIG. l at 33.

In order to extinguish the arc thus formed, a plurality of spaced-apart metal plates 34 have been stacked across the course of the arc above the arcing chamber defined by the sidewalls 21 and 22. The extending arc impinges upon the exposed leading edges 3S (see FIGS. 3 and 4) of these metal (preferably steel) plates and is chopped or divided thereby into a family of serially related sections which are rapidly deionized and extinguished in accordance with the theory discussed above in the introduction of this specification. y

In order to provide an exceptionally large number of metal plates and rto obtain quick entry by the arc into the interplate spaces, the plates are arranged in two groups 36 and .37 along the periphery of the arc loop. As is clearly shown in FIG. l, the plates 34 of each of the groups 36 and 37 lare stacked in parallel planes, and the two groups are tilted relative to each other so that the planes of their respective plates are generally perpendicular to the loop-shaped course of the arc 33.

Preferably each group 36, 37 of metal plates 34 is organized as a separate sub-assembly comprising: a pair of spaced sidewalls 3S and 39 of a suitable insulating material; a pair of transverse endwalls and 4l disposed between the sidewalls 3S` and 39 at opposite ends thereof and fastened thereto by sets of bolts l2 or the like; and a pair of retaining bar-s 43 located at the top of the sidewalls 3S and 39, respectively, and fastened to both end-v walls dil and ll by suitable means such as the bolts ed shown in FIG l. The opposing inner faces of the sidewalls 3S and 39 are respectively provided with appropriate grooves or slots for receiving opposite ends of each of the metal platesd which are located in the same sub-assembly. The metal plates, -which span the sidewalls, arev locked -in position by theretaining bars 43, and the lower portion of each plate is centrally recessed or notched so that its leading edge defines an inverted V, as is best seen in FIG. 4.

Each sub-assembly or group 36, 37 of the metal plates 34 is fitted into the arc extinguisher .ll between upwardly projecting portions of the bracing plates 7.6 and 2.7 where it is `fastened by means of the lower one, of each set of bolts`42. The sidewalls 21 and 22 of the extinguisher are provided with nesting recesses at i5 along their top edges, and corresponding tongues at the bottoms of the sidewalls 38 and 39 are snugly received inthe recesses 45 as indicated in FIGS. l and 2. It is apparent in FIG. 2. that the sidewall 3S is in effect an extension of the sidewall 2l, while the sidewall 39 is in effect an extension of sidewall 2.2, and these respectively mating sidewalls are considered in essence to be one and the same for the purposes of the appended claims.

Because of the disposition of the two metal-plate subassemblies .36 and 37, and in order to enlarge the venting area in the region of the arc extinguisher which is most remote from the region of arc initiation, the metal plates 34a and 34h at the proximate ends of the two groups 36 and 37, respectively, are not parallel and are separated by a gap which is larger than the interplate spacings within the subassemblies 36 and 37. This gap, as can plainly be seen in FIG. l, has a tapered conliguration, the breadth of the gap progressively increasing toward its outward or discharge end. With this arrangement a possibility exists that the arc section extending between the end plates 34a and 3.411 might undesirably blow entirely through the enlarged gap prior to complete extinction of the arc. To minimize such a possibility we have disposed in the gap between the end plates 34a and F24-b an arc-intercepting metal member 46 which can be constructed of magnetizable material such as steel. The member d6, as is shown in FIGS. l-3, has the preferred shape of a thick walled, short tube or ring, with the axis of its circular periphery being oriented generally perpendicular to the sidewalls of the arc extinguisher, and it serves in a manner to be explained more fully hereinafter to contain the arc within the gap between the proximate ends of the two groups of metal plates.

As is best seen in FlGS. l and 2, the metal ring or arcintercepting member 'do is supported centrally between the end plates 34a and Ele-b and centrally between sidewalls 38 and 39 by means of an insulating block 47 which secured by lmeans of a pin 49 extending through a bushi ing 'Sd of suitable insulation. Thus the ring 46 is separated from both sidewalls by insulating media. The axis of the ring lies on the bisector of the acute angle formed by the intersecting planes of the adjacent end plates 34a and Sflb, which bisector is normal to the loop-shaped course of the arc, and the ring i6 is -so located in the space between end plates that the arc impinges upon it approximately at the same time lthe exposed leading edges 35i of the two end plates are impinged upon.

The manner in which the arc-intercepting metal ring 46 is able to control the arc within the gap between the end plates 34a and Sti-b will now be explained with particular reference to FIG. 3. ln FIG. 3 the arc identified by the reference number 5i has been driven against the exposed leading edges 35 of the metal plates and against a point 46a of arc impingement on the ring 46, and it is here shown just prior to being divided by these metal parts into a family of serially related sections. The ring 46 causes the arc section extending between the end plates 34a and 34h to be divided into two arclets which will move through the spaces between the end plates and the respectively adjacent sides of the ring to positions of equilibrium indicated at S2 and 53.

lt will be observed in FIG. 3 that the opposite sides of the ring 4.6, considered from the point @da of arc impingement to points in closest proximity with the adjacent end plates, respectively, are disposed in outwardly converging relationship with the end plates 34a and 34h, respectively. The distances which the arcle-t terminals attached to the ring must travel along the ring surface between the aforementioned points are considerably longer than the surface distances from exposed edge 35' to points, on the respectively adjacent end plates, in closest proximity with the ring. 4As a result, the arclet terminals attached to the ring advance normally to the loop-shaped course of the arc at a slower rate than the arclet terminals attached to the end plates, and a concavity is created in the arc loop. ln other words, the two arclets 52 and 53 in the gap between the end plates Elia and 34b will form a reverse minor loop which is concave relative to the outwardly expanding major loop formed by the arc sections within the adjoining stacks 36 and 37 of spaced metal plates. Due to the magnetic effect of this concavity, the generally outwardly directed expansion of the arc is neutralized, and the arclets 52 and 53 will seek the positions of equilibrium as shown.

The preferred ring-like shape of the arc-intercepting member lo is particularly desirable from the point of view of the effective performance of its arc holding function. The current which passes through the body of the ring ed between the arclet terminals attached to its opposite sides will follow in varying proportions two parallel, gel erally semicircular paths. This contributes to the acuteness of the minor are loop within the gap between end plates 34a and 3ft-b, and local magnetic effects of the minor loop are correspondingly augmented. As a result, the forces acting on the arclets 52 and 53 due to the local magnetic effects are strengthened, and the equilibrium positions of these arclets are made more definite.

It is now apparent that 'the arc is stabilized by the ring 46 -between the two groups 36 and 37 of spaced metal plates, with all of the metal plates in both groups being fully utilized. By using a ring 46 of relatively short axial length, the arc is also stabilized midway between the insulating sidewalls of the arc extinguisher 11, and this minimizes the undesirable erosion and gasing of the insulating material which would occur should the arc move into close proximity with the inner surface of either one of the sidewalls.

7 For the purpose of inhibiting the re-establishment or restriking of an arc across the trailing edges of the metal plates 34 as the arc gasesv leave the interplate spaces following arc extinction, predetermined plates are made shorter than others and baffle members or plates 54 of insulating ma-terial are disposed, respectively, in edgewise association with the trailing edges of the short metal plates. Preferably every other metal plate 34 in each of the two stacks 36 and 437 is a short plate backed up by one of the insulating plates 54. The insulating plates 54 span the sidewalls 38 and 39 between alternate plates 34 and the exhaust outlet of the arc extinguisher 11 in generally coplanar relationship, respectively, with these short metal plates. Such an arrangement is fully described and is claimed in the aforesaid Stewart Patent 3,031,552. In accordance with our invention, the junction between the associated metal and insulating plates 3'4 and 54 is specially configured, as is best seen in FIG. 4, in order to assist the metal ring 46 in stabilizing the arc sections midway between the arc extinguisher sidewalls.

In FIG. 4 a short metal plate 34 and the insulating plate 54 in edgewise association therewith have been shown. Both of these plates have substantially the same thickness. The insulating plate 54 includes along Vits vertical edges keying recesses 55 into which fit the retaining bars 43, and in this manner the insulating plate is locked in position when assembled in a stack of metal plates. The lowerv part of the insulating plate 54, as is best seen in FIG. l, overlaps the trailing portions of the regular metal plates which are adjacent to each of the short plates.

As is shown in FIG. 4, the upper or trailing edge of the short metal plate 34 has a generally convex contour, and the cooperating edge of the associated insulating plate 45 has a matching concave contour. Although arcuated contours are shown, the desired results do not depend on the use of this particular conliguration. The corresponding convex and concave contours could be trapezoidal or the like. The important criterion is that the trailing edge of the short metal plate be more remote from the region of arc initiation, at a point 56 midway between sidewalls, tha-n it is at points next to the sidewalls of the arc extinguisher. With this construciton, the arc sections attached to each of the short metal plates will be maintained equidistantly between the insulating sidewalls as they attain the trailing edge of the plate at the extreme outward expansion of the arc loop.

While a preferred form of the invention has been shown and described by lway of illustration, many modifications will occur to those skilled in the art. Therefore,` we contemplate by the concluding claims to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric circuit interrupter including contact structure for establishing an arc which follows an expanding loop-shaped course from the contact structure, an arc extinguisher comprising: means including a pair of spaced sidewalls for enclosing the arc; a plurality of spaced-apart metal plates spanning the sidewalls across the course of the arc so as to divide the arc into a family of serially related sections, said plates being arranged in at least two groups with the plates comprising each of said rgroups being substantially parallel to each other and generally perpendicular to said loop-shaped course, the plates, at the proximate ends, respectively, of the two groups being nonparallel and being spaced from each other by a gap which is larger than any of the interplate spacings within said groups; a metal ring; and means including a bushing of insulating material within said ring for suspending the ring wholly within said gap with its axis oriented generally perpendicular to said sidewalls, whereby the arc section extending between said proximate end plates is intercepted by the ring and contained thereby in said gap. Y 2. In an electric circuit interrupter including contact structure for establishing an arc which will `follow an expanding generally loopshaped course, an arc extinguisher comprising: means including a pair of spaced sidewalls for enclosing the arc; means comprising a plurality of spaced-apart metal plates spanning the sidewalls across the course of the arc for chopping the arc into serially related sections, said plates being arranged in at least two groups so disposed with respect to each other that the plates at the proximate ends, respectively, of the two lgroups are separated by a tapered lgap; and arc-intercepting metal means in said gap for dividing the arc section extending between said end plates into two arclets, said means being so constructed and arranged in relation to said end plates that the terminals of said arclets attached to it advance normally to the loop-shaped course of the arc at a slower rate than the arclet terminals attached to said end plates, respectively, thereby creating in said gap a concavity in the arc loop which concavity is effective to stabilize the arc in the gap.

3. In an electric circuit interrupter including contact structure for establishing an arc which will yfollow an outwardly expanding :generally loop-shaped course from the vicinity of the contact structure, an arc extinguisher comprising: means including a pair of spaced sidewalls for enclosing the arc; a plurality of spaced-apart metal plates spanning the side walls across the course of the arc so that the arc impinges upon expo-sed edges of the plates and is divided thereby into serially related sections, said plates being arranged in two groups with the plates comprising each of the groups being generally perpendicular to said loop-shaped course, and with the two plates at the proximate ends, respectively, of said groups being separated by a gap of outwardly increasing breadth;

an arc-intercepting metal member; and means locating said member within said gap for impingement by the arc approximately at the same ytime the exposed edges of said two end plates are imp-inged upon, said member having non-parallel opposite sides disposed in outwardly converging relationship with said end plates, respectively, the conlgurat-ion of each of said lopposite sides being such that its surf-ace distance `from the point of arc impingement on said member to a point in closest proximity with the kadjacent end plate is longer than the distance between the exposed edge of said adjacent end plate and a point on sai plate in closest proximity with said member, whereby the `arc is stabilized within said gap and prevented from blowing therethrough.

4. In an electric circuit interrupter including contact structure -for :establishing an a-rc which will follow an expanding generally loop-shaped course, Ian arc extinguisher comprising: means including a pair of spaced sidewalls generally parallel to the course of the arc for enclosing the same; means comprising a plurality of spaced-apart metal plates spanning the sidewalls across the course of the `arc for chopping the arc into serially related sections, said plates being arranged in at least two groups with the plates in each of the groups being generally perpendicular to said loop-shaped course and with the plates at the proximate ends, respectively, of the two groups being separated by a space which is larger than any of the interplate spaces within said groups; and means comprising an arc-intercepting metal member disposed in said space between said proximate end plates for causing the arc section extending between said end plates to be ldivided into two arclets, said member having a generally circular periphery the axis yof which is oriented perpendicular to said sidewalls, between which the member is centrally located, and having an axial length substantially shorter than the distance which'separates the sidewalls, whereby the are section in said space is sta- MAI" bilized centrally between said sidewalls and is prevented from blowing through said space.

5. ln an electric circuit interrupter including contact structure for establishing an arc which will 'follow an expanding generally loop-shaped course, an arc extingu-isher comprising: lmeans including a pair of spaced sidewalls for enclosing the arc; at least two groups of spaced-apart metal plates spanning the sidewalls across the course of the arc so as to chop the arc into serially related sections, the plates in each of the two groups being stacked in parallel planes with the two plates at the proximate ends, respectively, tot the groups rlying in planes dening an acute angle the bisector of which is normal to the loop-shaped course of the are; and means comprising an arc-intercepting metal member centrally located between said two end plates, and separated trom said sidewalls by insulating media, for dividing the are section between said end plates intotwo arclets, saidV member being so shaped that the terminals of said arclets attached to it advance normally to the loop-shaped course of the arc at a slower rate than the arclet terminals attached to said end plates, respectively, thereby creating between the two groups of plates a concavity in the arc loop, whereby the arc will be contained between said end plates in spaced relation to said sidewalls.

6. In an electric circuit interrupter including contacts separable to initiate an arc which will `follow an expanding generally loop-shaped course from the region of arc initiation, an arc extinguisher comprising: means including a pair of spaced sidewalls dening an arcing chamber in the vicinity ofthe region of are initiation; means comprising a plurality of spaced-apart metal plates spanning the sidewalls across the course of the arc so that the are :impinges upon the exposed leading edges of the metal plates and is divided into serially related secl@ tions, said plates being arranged in at least two groups with plates at proximate ends, respectively, of the two groups being spaced from each yother by a tapered gap which is larger than any interplate spacing in either group of plates, at least one of the lmetal plates between opposite ends of each of sia-id groups having in edgewise association with its trailing edge an insulating plate spanning the sidewalls in generally coplanar relationship with said one lmetal plate, said trailing edge having a generally convex contour and the cooperating edge of the associated insulating plate havin-g a matching concave contour, so that midway between said sidewalls said traiing edge -is more remote from ysaid region of arc initiation than are portions of the trailing edge next to the sidewalls; and a magnetizable metal ring disposed `in said tapered gap with its axis `oriented generally perpendicular to said sidewalls, the `axial `dimension `of the ring being shorter than the -distance between the sidewalls and the ring being separated yfrom both sidewalls by insulating media, whereby the :arc section extending between said proximate end plates impinges upon said ring and is thereby stabilized in said gap midway between said sidewalls.

References Cited in the file of this patent UNITED STATES PATENTS 1,483,431 Hall Feb. 12, 1924 1,868,442 `Corbett July 19, 1932 2,147,419 vBaker Feb. 14, 1939 2,180,147 Hopp Nov. 14, 1939 2,243,039 Ludwig et -al May 20, 1941 2,861,152 Scully Nov. 18, 1958 FOREIGN PATENTS 1,113,443 IFrance Dec. 5, 1955 

1. IN AN ELECTRIC CIRCUIT INTERRUPTER INCLUDING CONTACT STRUCTURE FOR ESTABLISHING AN ARC WHICH FOLLOWS AN EXPANDING LOOP-SHAPED COURSE FROM THE CONTACT STRUCTURE, AN ARC EXTINGUISHER COMPRISING: MEANS INCLUDING A PAIR OF SPACED SIDEWALLS FOR ENCLOSING THE ARC; A PLURALITY OF SPACED-APART METAL PLATES SPANNING THE SIDEWALLS ACROSS THE COURSE OF THE ARC SO AS TO DIVIDE THE ARC INTO A FAMILY OF SERIALLY RELATED SECTIONS, SAID PLATES BEING ARRANGED IN AT LEAST TWO GROUPS WITH THE PLATES COMPRISING EACH OF SAID GROUPS BEING SUBSTANTIALLY PARALLEL TO EACH OTHER AND GENERALLY PERPENDICULAR TO SAID LOOP-SHAPED COURSE, THE PLATES, AT THE PROXIMATE ENDS, RESPECTIVELY, OF THE TWO GROUPS BEING NONPARALLEL AND BEING SPACED FROM EACH OTHER BY A GAP WHICH IS LARGER THAN ANY OF THE INTERPLATE SPACINGS WITHIN SAID GROUPS; A METAL RING; AND MEANS INCLUDING A BUSHING OF INSULATING MATERIAL WITHIN SAID RING FOR SUSPENDING THE RING WHOLLY WITHIN SAID GAP WITH ITS AXIS ORIENTED GENERALLY PERPENDICULAR TO SAID SIDEWALLS, WHEREBY THE ARC SECTION EXTENDING BETWEEN SAID PROXIMATE END PLATES IS INTERCEPTED BY THE RING AND CONTAINED THEREBY IN SAID GAP. 